Optical sampling oscilloscope utilizing organ arrays of optical fibers

ABSTRACT

An organ array comprises a plurality of optical fibers each cut to a different length with the differences between functionally adjacent (i.e., lengthwise consecutive) fibers being uniform. The fibers are arranged in a bundle so that one set of ends of the fibers is terminated in an input plane and the opposite set of ends is terminated in an output plane. Described are several embodiments utilizing the organ array including a passive spatial scanner, optical memory systems, an image converter, an optical sampling oscilloscope, and an x-y coordinate locater.

`lR 131%51721 d`msm`` [45] Dec. 9, 1975 Duguay [54] OPTICAL SAMPLINGOSCILLOSCOPE 3,596,104 7/1971 V11/1ac01r1be1 25o/227 UTHLIZING ORGANARRAYS 0F OPTICAL MBERS Primary Examiner-R. V. Rolinec [75] Inventor:Michel Albert Duguay, Summit, N.J. Assistant Examiner-Ernest F. KarlsenU [73] Assignee: Bell Telephone Laboratories, Attorney Agent or Flrm M Jrbano Incorporated, Murray Hill, N.J.

[22] Filed: Mar. 10, 1975 [57] ABSTRACT [21] Appl' NO': 556636 An organarray comprises a plurality of optical fibers Related U.S. ApplicationData each cut to a different length with the differences betweenfunctionally adjacent (.e., lengthwise consecutive) fibers beinguniform. The tibers are arranged in a bundle so that one set of ends ofthe fibers is termi- [62] Division of Ser. No. 401,635, Sept. 28, 1973.

[52] U.S. Cl 324/121 R; Z50/227; 333/29; n

35o/96 B nated 1n an lnput plane and the opposlte set of ends 1s [51]im. CL2 G01R 13/20; G02B 5/14 terminated in an Output Plene- Describedare Several [5s] new of Search 324/121, 77 A; 35o/96 B; embodimentsutilizing the Organ army including a P2S- 333/29; 250/227; 328/151;315/379, 383 sive spatial scanner, optical memory systems, an imageconverter, an optical sampling oscilloscope, and an x-y coordinatelocater.

[56] References Cited UNITED T E P S AT S ATENTS 6 Claims, 10 DrawingFigures 3,278,846 lO/l966 Patten et al 333/29 PASSIVE SCANNER l5 ORGANF1BER ARRAY 24 OBJECT PLANE sHuTTER 1e ORGAN HEER V l VOLA L ARRAY14 4216 24.1 995115 I r16.315,4,r 116.2 :14.1 500115 1 ,L/s1111Lu l 1111 1.1 es |242 99ops 1 1 114.2 495115 1r www.- 1 1 1\ 1111111.111LLLEm m e 11 './L111111111 111111 1 1 /l 11 il 1 Q9 510115 1 1/' 7 11499 n l' 'n E`lr@24.99 505m |V iI/, 1011s g 5 24.100 4 c y/ /500p5 l l, 1 10o L A4f il RULSED/IO I L1GHT souRcE 1B 13 l coNTRoL T11/11N@ PULSE 1 -5oon5 REALNME-+1 MEANS LASER 2e ELEcTRomc osclLLoscoPE souRcE 111s R1sET1ME 3oRECORDING MEANS U.S. Patent Dec. 9, 1975 sheer 2 @f4 3,925,727

MEMORY SYSTEMS VERTICALLY MOVING vTOEO TAPE OO P HORIZONTAL lm/ COUPLTNOI lwATT ARRAY @5 IOAlm SEO. `OPTICS TO 72 l B65 Til@ T65-.T ,-g/ f) fl t,lfffguzsl i 2 @565.33m r PJTLOSHET) 'i Q99 CAOS, PHOTO- SOURCE T l l i(TOOkHz) g i LTR g l OIOOE `O OOUPLING @o 'om 3|* i OPT|cs 63 Lut-"I 64IO/um 68 V* J 0(0)\0"\ PAsslvE SCANNER OO GATE CULI; 421i Somv A t l-O.I/us

I sHuTTER 94 v A S48 9o 89 92 ,-glifI--I /96 PHOTO- 'I I O|OOE` l I I II l I i i 94ml] 59M km" l .J

59m A94 B94 SIOO U.S. Patent Dec. 9, 1975 sheet 3 @f4 3,925,727

mzmm wf m5 @222% 3mi if Il SHI-lillldS WVIE Sheet 4 0f4 t=0 500ns ik* w4% 11X H+ U.S. Patent Dec. 9, 1975 OPTICAL SAMPLING OSCILLOSCOPEUTILIZING ORGAN ARRAYS OF OPTICAL FIBERS CROSS REFERENCE TO RELATEDAPPLICATIONS This application is a division of parent application Ser.No. 401,635 filed on Sept. 28, 1973 and was concurrently filed with twoother divisional applications of the same parent: divisionalapplications Ser. No. 556,637 entitled Optical Memory Systems UtilizingOrgan Arrays of Optical Fibers and Ser. No. 556,638 entitled OpticalDetection Systems Utilizing Organ Arrays of Optical Fibers.

The parent application was concurrently filed with two relatedapplications: Ser. No. 401,633, now U.S. Pat. No. 3,838,278 issued onSept. 24, 1974 entitled Optical Switching Networks Utilizing OrganArrays of Optical Fibers and Ser. No. 401,632, now U.S. Pat. No.3,849,604 issued on Nov. 19, 1974 entitled Time Slot lnterchanger forTime Division Multiplex System Utilizing Organ Arrays of Optical Fibers.

BACKGROUND OF THE INVENTION This invention relates to arrays of opticalfibers, and, more particularly, to passive spatial scanners, opticalmemories, image converters and other optical apparatus utilizing same. Y

Optical memories proposed by many workers in the laser art typicallyinclude an optical scanner to perform the necessary read and writefunctions. Most commonly the scanner utilizes an active device, such asan electro-optic or acousto-optic modulator, to deflect a laser beam inraster fashion. In this type of active scanner, however, importantparameters such as bandwidth, the number of resolvable spots, and drivepower involve numerous trade-offs which, in conjunction with inherentmaterials restrictions, limit their usefulness in optical memories aswell as in numerous other applications including real-time displaydevices, hard copy reproduction devices, carrier modulators and thelike. Described hereinafter, however, is a passive scanner in accordancewith my invention which reduces significantly many of the foregoingproblems encountered with active scanners.

Similar trade-offs arise in the design of image converters, especiallywhere the image to be detected is virtually instantaneous. Anexample ofthe latter is a picosecond light pulse. ln recent years many techniqueshave been developed to display and measure such light pulses; e.g.,two-photon fluorescence, picosecond streak cameras, light-in-flightphotographic techniques and echelon techniques, all of which typicallydisplay the pulse on photographic film. Unfortunately, the nonlinearityand limited dynamic range of fast photographic film entailtime-consuming photodensitometry and limit the practical usefulness ofthese methods. Although picosecond pulses can also be measured utilizingsecond harmonic generation, many laser shots are required so that it maytake several hours to obtain one pulse display. The problem is furthercompounded by the irreproducibility of present high-powerpicosecondpulse lasers. Described hereinafter, however, is an opticalsampling oscilloscope in accordance with my invention which givesinstantly a linear display of a single picosecond pulse on a nanosecondreal-time oscilloscope.

SUMMARY OF THE INVENTION As used hereinafter, an organ array of opticalfibers comprises a bundle of optical fibers each having a differentlength with the difference in length between functionallyadjacent-fibers being uniform. The term functionally adjacent meanslengthwise consecutive and includes, for example, in a raster of fibersnot only fibers physically adjacent one another in the same row,

but also fibers physically remote such as the last fiber of one row andthe first fiber of the next row. The organ array is furthercharacterized in that one set of fiber ends is terminated in an inputplane and the opposite set of ends is terminated in an output plane. Thetwo planes need not be parallel, nor even planar in the geometric sensesince either set of ends can terminate on acurved surface or even in anincoherent array of points.

In an illustrative embodiment of my invention, a passive optical scannercomprises a pulsed light source, such as an LED or a laser, means forproducing a plurality of spatially separated light pulses from eachlight pulse generated by the pulsed source, and means for coupling eachof the spatially separated pulses into separate ones of the fibers ofthe organ array at its input plane. Because the differential fiberlength produces a proportional differential time delay, a plurality ofpulses, substantially identical in transverse shape to the sourcepulses, appear at the output plane at different times and in differentspatial locations.

My passive optical scanner involves no deflection of a laser beam butinstead employs a unique combination of elements including anorgan arrayof optical fibers to produce linear or raster scanning of light pulses.The number of resolvable spots is determined primarily by the diameterof the fibers and the coupling optics, the scanning rate is determinedprimarily by the differential length of the fibers, and the spatialscanning range is determined primarily by the spatial pattern of theoutput ends of the organ fiber array. Also the scanning is done indiscrete steps; i.e., if a row of discrete spots on a target is to bescanned', light appears sequentially only at those spots, and noneappears at intermediate positions. l

The essence of this'embodiment of my invention, therefore, lies in therecognition that a pulsed optical source in conjunction with a suitablepassive device produces scanning, a dynamic function,

My optical scanner can be utilized to perform a scanning function in amemory system in which, for example, a translating memory tape orrotating disc is juxtaposed with the output plane of an organ array toread out information on the tape or disc, or in conjunction with asuitable modulator, to write. information onto the tape or disc.

When combined with other components, my scanner can also be utilized toperform a variety of display functions. Thus, for example, when thetandem combination of a second organ array and an optical gate isinterposed between the pulsed light source and the first array, thearrangement functions as an optical sampling oscilloscope capable ofdisplaying sub-nanosecond optical pulses with picosecond resolution onan electronic oscilloscope having only nanosecond risetime.

In addition, a two-dimensional organ fiber array can be utilized as anx-y coordinate locater by positioning the input planes of twointerleaved organ arrays, each having a mutually exclusive set ofdelays, under a writing surface. One array of fibers corresponds to thex coordinates and another set of fibers corresponds to the ycoordinates. A pulsed light pen (e.g., a pulsed laser) directs a spot oflight of sufficient size on the writing surface to overlap at least twofiber ends of adjacent fibers in different arrays. The outputs of botharrays are coupled to a photodiode which produces electrical pulseswhose times of occurrence are a function of the position of the lightspot in the x-y plane. These times of occurrence relative to the firingtime of the light pen can be coded in the form of digital electronicpulses. Consequently, information which is written by the light pen isconverted to a digital form suitable for transmission to a remotelocation.

The foregoing locater is a special case of an image converter alsodescribed.

BRIEF DESCRIPTION OF THE DRAWING My invention, together with its variousfeatures and advantages, can be easily understood from the followingmore detailed description taken in conjunction with the accompanyingdrawing, in which:

FIG. l schematically shows a passive optical line scanner in accordancewith an illustrative embodiment of my invention;

FIG. 2 schematically shows a two-dimensional organ array of fibers forproducing raster scanning',

FIG. 3 schematically shows a memory system in accordance with oneembodiment of my invention;

FIG, 4is a graph showing a typical output of the photodiode of FIG. 3;

FIG. 5 schematically shows an optical sampling oscilloscope inaccordance with another illustrative embodiment of my invention',

FIG. 6 is a graph depicting the manner in which the optical gate I6 ofFIG. 5 samples the pulses delayed by organ fiber array M of FIG. 5;

FIG. '7 schematically shows an image converter in accordance with stillanother embodiment of my invention;

FIG. 8 schematically shows an x-y coordinate locater in accordance withyet another embodiment of my invention;

FIG. 9 is a schematic side view showing a preferred arrangement of thefibers under the writing surface of FIG. 8; and

FIG. l() is a graph showing a typical electrical output from thephotodiode of FIG. 8.

DETAILED DESCRIPTION Passive Scanner Turning now to FIG. l, there isshown a passive line scanner illustratively comprising a pulsed lightsource l0, such as a laser or an LED, the collimated output of which isdirected through a plurality of tandem beam splitters Il which produce acorresponding plurality of light pulses from each source pulse generatedby source lli). The plurality of light pulses propagate along separatenoncollinear paths to a lens means l2 which focuses the pulses onto theinput plane A of an organ fiber array llt, the input plane A beingpositioned at the focal point of lens means l2.

The organ fiber array I4 comprises a bundle (of plurality n) of opticalfibers each having different lengths, with the difference in lengthbetween lengthwise consecutive (i.e., functionally adjacent) fibersbeing uniform. Thus, fiber f4.1 is depicted as having length L.

4l adjacent fiber 14.2 has a length (L -lwhereas fiber 14.11 has alength (L+ (n-l )5). In addition, one end of each of the optical fibersis terminated in the input plane A, whereas the opposite ends areterminated in an output plane B, but the planes A and B need not beparallel.

Because the uniform difference in length of the fibers of array 14produces a proportional uniform difference A1' in time delay, each ofthe plurality of light pulses arrives at the output plane B at differenttimes (corresponding to the difference Ar) and in a different spatiallocation (corresponding to the locations in space of the output ends ofthe fibers).

Note that, in general, one skilled in the art would typically take intoaccount the different path lengths from the source l0 through the beamsplitters 11 and lens means l2 to input plane A in making thedifferential delay Ar uniform. Moreover, for efficient optical couplingthe directions of the pulses may be made collinear with the directionsof the fiber ends at input plane A. In addition, dispersion introducedby the fibers may be readily compensated by means well known in the art,e.g., by means of grating-pairs or Gires-Tournois interferometers.

Advantageously, the pulses arriving at output plane B are allsubstantially identical in intensity and transverse shape to oneanother; that is, recognizing that there are inherent optical couplinglosses, each pulse has an intensity equal approximately to n1 times theintensity of the source pulse generated by source 10, but has the sametransverse shape as the source pulse.

The net effect of this combination of elements is to produce adiscretely scanning spot of light, i.e., pulses of light which arrivesequentially at output plane B at locations corresponding to the outputof ends of fibers 14.1 to 14.11 in that order. Consequently, the entireline of spots between the first fiber and the nt" fiber is scanned in atime equal to (n-l )Ar For example, if a lOO ps pulse from a laser iscoupled into a fiber array I4 designed so that the differential lengthproduces a differential time delay A1' of 0.5 ns, then an array of lOlfibers would scan a line in 500 ns.

inasmuch as the output from an optical fiber typically has considerablebeam divergence, it may be desirable to position a lens means 22, orother suitable focusing means, between output plane B and an object 19to be scanned. In this regard, the lens means 22 should be positioned ata distance approximately equal to 2f from both plane B and object I9,where f is the focal length of lens means 22.

In general, however, to achieve scanning, it is desirable that thepulses arrive at output plane B with as little time-wise overlap aspossible; i.e., two or more pulses should not reach output plane B soclose in time to one another that both appear substantiallysimultaneously. To this end, the differential time delay Ar of array 14should be greater than the duration T of the source pulses as measuredat half-maximum intensity.

Advantageous aspects of my passive line scanner include the following'.(l) the output pulses arriving at plane B have substantially identicaltransverse shapes and substantially identical power densitydistributions thereby insuring that the effect of each output pulse on adetector or other utilization means is substantially the same.Consequently, additional components or circuitry are not required tocompensate for unwanted variations in power from one pulse to another',(2) the scanning function is performed without the necessity of 5deflecting the light beam; i.e., without using an active modulator.Instead scanning is performed passively by the unique combination of thebeam splitters 11, the lens means 12, and the organ fiber array 14; (3)in this regard the number of spots or information points resolvable bymy passive scanner is determined primarily' by the diameter of thefibers used; the scanning rate is determined primarily by the practicallimitations on producing small differential lengths and by the bandwidthlimitation of utilization means; and the scanning range (correspondingto the angular deflection in an active scanner) is determined primarilyby the spread of the output ends of the fibers in the output plane B;and (4) the scanning is done in spatially discrete steps, a highlydesirable feature in digital memories and for writing on color TVscreens.

For simplicity the foregoing embodiment of FIG. 1 was described in termsof a line scanner. However, it is readily possible to extend itsfunction to that of a raster scanner by utilizing a two-dimensionalarray of optical fibers as depicted in FIG. 2. For the purposes ofillustration, FIG. 2 shows a 5 5 square array of 25 optical fibers inwhich the first fiber is the rshortest and the 25"l is the longest. Asbefore, the fibers are cut so that the difference in length betweenfunctionally adjacent fibers is uniform. Fibers are shown schematicallyas straight lines with loops intermediate the ends. Longer fibers havemore loops than shorter fibers. This schematic representation isindicative of the fact that flexible optical fibers, often as thin ashuman hairs, could be wound on spools or other means in order to allowfor longer fibers to have their ends terminated in the same input andoutput planes as shorter fibers. Thus, for example, the difference inlength between fibers 1 and 2, 2 and 3, 3 and 4, and 4 and 5, whichconstitute the first row, is uniformly equal to Fibers l through 5 arenot only physically adjacent, but also are functionally adjacentinasmuch as it is intended that an output pulse arrive at the end offiber 1 first and that later pulses appear sequentially at the end offibers 2, 3, 4 and 5. Note, however, that fiber 6 (the first fiber inthe second row) is physically remote from but functionally adjacent tofiber 5 (the last fiber in the first row). Similarly, fibers l and 11are functionally adjacent. Consequently, the difference in lengthbetween fibers and 6, and between fibers 10 and 11, is also equal toWith this arrangement light pulses scan the output plane B in rasterfashion.

Memory Systems In some types of optical memories information is writtenonto a surface (e. g., tape, disc, or drum) and is accessed along one ortwo dimensions by deflecting a laser beam. With prior art activedeflection devices the scanning time is relatively slow; i.e., in theorder of microseconds. Considerably faster scanning times of the orderof nanoseconds should be achieved by utilizing the passive opticalscanner of my invention. Illustrative examples of the use of my passivescanner in optical memories and in apparatus for video tape read-out andwrite-in are given below.

In a video tape read-out arrangement shown in FIG. 3, a video tape 66carrying information in the form of 100 columns of dots 'f varyingoptical density (i.e., black, gray, transparent) on a transparentsubstrate (e.g., a film negative) moves vertically down at a modestspeed of, say, 1 meter/sec in front of a photodiode 72. The dots arearranged vertically in columns which are l0 pim apart and horizontallyin rows which are also l0 in apart. Disposed between the video tape 66and the photodiode 72 are an optional lens means 68 and coupling optics70 which might include, for example, a bundle of optical fibers. Theoptional lens means 68 would be used to couple light into such fiberswhen included in optics 70.

On the side of the video tape 66 remote from the photodiode 72 ispositioned a passive scanner 60 of the type described with reference toFIG. 1. As before, scanner 60 comprises a light source 61 whichgenerates illustratively a l watt pulse of 25 ns duration every lO its.Coupling optics 63, which schematically designates -i the beam splittersl1 and lens means 12 of FIG. 1, is

used to couple the pulses from'source 61 into a horizontally orientedorgan fiber array 65 comprising illustratively fibers cut to uniformlydifferent lengths to produce a uniform differential delay of 0.1 ys andtotal delays ranging from 0.1 las to 10 ys.

In operation, every 10 [.Ls laser 61 is pulsed for about 25 ns and thepulse generated is coupled into organ fiber array 65. The array 65 isarranged so that the first pulse to reach the output plane B65originates from fiber 65.1 and strikes a dot in column No. 1 of tape 66.Then 0.1 its later the second pulse to reach output plane B65 originatesfrom fiber 65.2 (0.2 its delay) and strikes a dot in column No. 2 and soon. In this regard, note that because of the combined effect of tapemotion and inversion in the lens 64, the end of ber 65.2 should be 0.1,um higher than that of fiber 65.1, the end of fiber 65.3 should be 0.2[.Lm higher than that of fiber 65.1, and so on, to allow matching ofeach light pulse with the dot to be addressed.

Effectively, therefore, a reading spot of light scans an entire row ofdots on the tape 66 every 10 ys. The light transmitted through tape 66is directed to a single photodiode 72, the output of which (shownillustratively in FIG. 4) is the video signal. Note that at the end ofIl0 its a new row has moved into position so that the combined effect ofthe tape translation at l meter/sec and the pulses scanning at a rate ofone row per l0 ,as effectively multiplies the tape speed by a factor ofone hundred; i.e., the ratio of the speed of the horizontally scanninglight spot (l0 )Lm/0.1 ps 100 m/sec) to the speed of the verticallymoving tape of lm/sec is one hundred.

In a similar fashion, translating video tape 66 could be replaced by arotating disc with the ends of the fibers of array 65 positioned alongthe grooves of the disc, thereby increasing the effective rotationalspeed of the disc. Therefore, the actual rotational speed required toachieve a particular read-out speed is reduced.

In order to perform video tape write-in, two modifications are made inthe system of FIG. 3. First, the lens means 68, coupling optics 70, andthe photodiode 72 can be omitted. Secondly, a gate 62, such as anelectrooptic modulator, is positioned between the output plane B65 ofarray 65 and the video tape 66. An information source (not shown) iscoupled to the gate 62 in order to transmit and/or block selected onesof the pulses generated by scanner 60. By means well known in the art,the information source is coordinated with the tape position so thatliglit pulses from scanner 60 impinge upon only preselected informationpoints; i.e., dots, in preselected rows and columns of tape 66.

In an application to computer memories, my passive scanner should attaingreater reading speeds than that which can be achieved using state ofthe art components (e.g., the use of a plurality of magnetic readingheads positioned proximate a rotating drum). In this embodiment, anarrangement substantially identical to FIG. 3 is utilized with thefollowing illustrative parameters: laser 61 generates pulsesapproximately 0.2 ns in duration, organ fiber array 65 comprises 104fibers cut to produce a uniform differential delay of 1 ns, and totaldelays ranging from l ns to l us, and the tape 66 translates at arelatively higher speed of 100 meters/- sec. With these parameters,therefore, a tape page can be defined as containing 1 megabit ofinformation in l cm2; that is, if the tape 66 is taken to be at least 10centimeters wide, then a page can be defined as a rectangular zone l0centimeters wide by l mm high which contains an array of dots of varyingoptical density spaced both horizontally apart and vertically apart byum so that l04 columns fit in the l0 centimeter dimension.

In order to insure that the pulse dispersion in the longer fibers isless than 0.5 ns, use of graded index (Selfoc) fibers or single modefibers in the entire array is preferred.

In this embodiment l04 fibers are used to scan 1 spot per nanosecond;that is, l04 spots in a row in l0 us. The photodiode 72 consequentlyprovides an electrical read-out at a rate of l gigabit per second.Because the tape (disc or drum) moves at 100 meters/sec, a spot or dotmoves l mm in 10 us, which is equivalent to 100 spot spacings (since thespots are 10 um apart). Because there are 100 consecutive rows of dotsin a page of data, as defined above, then one page passes the scannerevery 10 us. Which particular row will be read is determined by thefiring time of the laser 61. The word of interest in the row of 104 bitsto be read out can be selected again by timing means well known in theart; i.e., by measuring the time elapsed after the firing of the laser.

Sampling Oscilloscope The passive scanner of FIG. 1 can also be utilizedin an optical sampling oscilloscope illustratively depicted in FIG. 5.Consequently, components of FIG. 5 corresponding to those of FIG. 1 havebeen given identical reference numbers. The sampling oscilloscopecomprises a passive scanner and the tandem combination of a second organfiber array 24, an optical gate or shutter 16 and lens means 23interposed between lens means 12 and organ fiber array 14. Utilizationmeans illustratively comprising a photomultiplier 26 converts theoptical pulses at the output of array 14 to electrical signals which arecoupled to an electronic oscilloscope 28 and optional recording means30. In this arrangement the output plane B24 of the organ array 24coincides approximately with the object plane of lens means 23, whereasthe input plane A14 of organ array 14 coincides approximately with theimage plane of lens means 23.

As described in my U.S. Pat, No. 3,671,747, the shutter 16 typicallycomprises a medium 16.3 in which birefringence can be optically inducedby means of a high intensity, short duration, laser control pulse. Thismedium may be either a solid, such as glass, or a liquid, such as carbondisulphide. In either case, the medium 16.3 is disposed between a pairof crossed polarizers 16.1 and 16.2. Normally the gate is closed so thatplane polarized pulses transmitted through polarizer 16.1 are absorbedby polarizer 16.2. In order to open the shutter 16, a control pulse fromsource 18 is directed at a shallow angle through the medium 16.3 tooptically induce therein birefringence so that the polarization ofpulses arriving from array 24 is changed sufficiently' (i.e., preferablyrotated by to permit transmission through polarizer 16.2. In particular,it has been found that the shallow angle 0 between the direction of thecontrol pulse and the direction of the pulses being sampled should beless than about 0.1 radians and preferably the two directions should becollinear. However, to achieve collinear propagation would requireplacing beam splitters or other suitable means within the shutter 116.As a practical matter, it is more convenient to refect the control pulseoff a suitable mirror 20 oriented to direct the control pulse onto themedium 16.3 at the desired shallow angle. In order to preventtransmission of the control pulse into the other components of thesystem, a rejection filter 16.4 is positioned between medium 16.3 andpolarizer 16.2. For example, where the pulse being sampled is red light(eg, wavelength of 0.63 um) and the control pulse is infrared (e.g., the1.06 ,um output of an NdzYAG laser), then a suitable filter is No. KG3manufactured by Schott Glassverk, West Germany.

The light pulse to be sampled and displayed is generated by source 10,and as before is directed through a plurality of beam splitters 11. Lensmeans 12 focuses the plurality of pulses generated by beam splitters 11onto the input ends of the fibers of array 24 at input plane A241 whichis positioned at the focal point of lens means 12. In order tosynchronize the arrival of the source pulse and the control pulse at themedium 16.3 of shutter 16, there is provided timing means 13 whichCouples together source 10 and control source 18.

In order to obtain picosecond resolution, both the differential delay ofthe fibers of array 24 as well as the duration of the control pulse istypically a few picoseconds.'I-Iowever, in order that a commerciallyavailable real-time electronic oscilloscope 28, typically having a onenanosecond risetiine, can display the sampled pulses, the differentialdelay of the fibers of array 14 is typically a few nanoseconds. Inaddition, the array is arranged to introduce complementary delay: thatis, a pulse experiencing the longest picosecond delay in array 24 iscoupled to the shortest fiber in array 14 so that in the latter array itexperiences the shortest nanosecond delay and conversely.

In general, the differential delays AT1., and L11-24 of organ arrays 14and 24, respectively, are chosen to Satisfy the following inequalities:

where T is the duration of the pulse to be sampled as measured at halfmaximum intensity, TS is the sampling time (i.e., the time for whichshutter 16 is open) and TR is the risetime of photornultipiier 26 and/orelectronic oscilloscope 28. Inequality (l) means that the plurality ofpulses arriving at shutter 16 (le, at medium 16.4) spatially overlap onseparate channels. Inequality (2) means that in reconstructing the shortduration (eg. 200 ps) sampled pulse on a longer time scale (e.g., 500ns), the samples are each delayed by an amount greater than theirduration (which corresponds to the sampling time plus any broadening dueto dispersion in the fibers). And, inequality (3) means that thereconstructed samples arrive at photomultiplier 26 and/or oscillo- 9scope 28 at a rate longer than the risetime (.e., within the bandwidth)limitations of such apparatus.

The operation of my sampling oscilloscope can be readily understood fromthe following description in which numerical parameters are provided forthe purposes of illustration only and are not to be construed aslimitations upon the scope of the invention. Consider, therefore, thatit is desired to display a red optical pulse having a wavelength atabout 0.63 ,um and a duration of approximately 200 ps as measured athalf-maximum intensity. This pulse is divided into a plurality of 100pulses of substantially identical transverse shape, but of lower peakpower, by means of 100 beam splitters 11. These pulses propagate alongseparate optical paths and are focused by means of lens means 12 ontoseparate ones of the fibers of organ array 24. Organ array 24 comprises100 low dispersion fibers cut to different lengths to provide delays indecrements of ps. For example, fibers 24.1, 24.2, 24.100 provide,respectively, delays of 995 ps, 990 ps 500 ps. The output of organ array24 at any particular instant of time constitutes a plurality of pulseson separate parallel paths (channels), with the differential delaybetween pulses in adjacent channels being 5 ps. These pulses are passedthrough an optical shutter 16 utilizing a l cm long carbon disulphidemedium 16.3. The framing (.e., sampling) time of the optical shutter isdetermined primarily by the duration of the 1.06 um control pulse whichis typically 5 ps. At any particular instant of time, therefore, theplurality of delayed pulses appearing at medium 16.3 are distributed inspace as illustratively depicted in FIG. 6. Therefore, when the gate isopened for approximately 5 ps by the control pulse, a plurality of timecoincident samples of 5 ps duration and of varying heights istransmitted through polarizer 16.2. These samples are designated in FIG.6 as S100, S99, S98 corresponding to the samples derived from fibers24.100, 24.99, 24.98 respectively. Thus, light pulses on the variouschannels are sampled at different sampling times for each channel butall 100 channels are sampled at the same real time.

These time coincident samples are now inversely delayed in order toreconstruct the original shape of the 200 ps pulse to be displayed. Tothis end the time coincident samples are coupled through lens means 23to the input plane A14 of organ array 14. In the latter array 100 fibers14.1, 14.2 14.100 are cut to provide delays in decrements of 5 ns. Thus,fibers 14.1, 14.2 14.00 have respectively delays of 500 ns, 495 ns 5 ns.The coupling optics are such that only light from the ml fiber in organarray 24 is coupled into the n"L fiber of the organ array 14. Thus, forexample, light from fiber 24.1, which experienced a 995 ps delay, iscoupled into fiber 14.100 where it experiences only a 5 ns delay. Incontrast, light from fibers 24.100 which experienced a 500 ps delay iscoupled into fiber 14.1 where it experiences a 500 ns delay. Each fiberin organ array 14 receives substantially simultaneously (noting thedifferent path lengths through lens means 23) a 5 ps sample of red lightand the n"l fiber 14.11 gives rise (n X 5) ns later to an electricalpulse about 2 ns at halfheight characteristic of the response time ofphotomultiplier 26. Note that the fibers of organ array 14 also have lowdispersion, .e., a 5 ps red sample typically broadens to less than l nson the longest fiber 14.1.

The function of the organ array i4 is to introduce a complementary delay(as compared to that introduced by array 24) and to place the samples ina nanosecond time domain compatible with the bandwidth of electronicoscilloscope 28 (e.g., a Tektronix 7904). Thus, the light coupledthrough organ array 14 is detected by a photomultiplier 26 of l nsrisetime and is displayed on an equally fast oscilloscope 28 which isset, for example, at a time sweep of 500 ns full scale. The envelope ofthe 100 pulses which appear on the screen 28.1 of oscilloscope 28represents the light signal that was incident on the organ array 24 inthe time interval 500 to 1000 ps prior to the opening of the shutter 16.Optional recording means 30 may include, for example, a camera or memorydevice for making a permanent record of the sampled pulse.

Image Converter There are instances where images recorded on film areformed in a time span of a few nanoseconds. This occurs, for example, inthe photography of ultrashort light pulses in flight (U.S. Pat. No.3,669,541), in photographing indoor scenes illuminated by nanosecondlight pulses, and more generally, in ultrahigh speed photography wherecameras are equipped with electrooptic shutters of nanosecond speed. Anorgan fiber array can be used, in place of photographic film, totransform the two-dimensional information present in an image, into asequence of analog electrical pulses for transmission over telephonelines or for storage in co mputer memories.

In an illustrative embodiment of an image converter shown in FIG. 7, anoptical image to be converted into an electrical analog is coupledthrough a nanosecond shutter 89 (e.g., an electro-optic shutter), andlens means 92 to the input plane A94 of an organ fiber array 94 adaptedto produce a uniform differential delay Ar94. In essence, the imageself-scans in that different spatial portions (.e., samples) of theimage are coupled into separate fibers of array 94. These samples aredifferentially delayed in array 94 and are then coupled to a suitabledetector such as photodiode 96. The output of photodiode 96 is a singlebus 98 on which appears in time sequence a plurality of samples spacedfrom one another by Ar94 which is made to be greater than the risetimeof photodiode 96.. Of course, the samples vary in intensity according tothe spatial intensity distribution of the image 90.

A special case of the foregoing is the x-y coordinate locater describedbelow.

The x-y Coordinate Locater This embodiment of my invention utilizes theability of an organ fiber array, when excited by a pulsed laser, to codeone dimension into a time interval. Two such arrays, therefore, can beused to code the position of a light pulse in two dimensions asillustrated in the following example of an x-y coordinate locater. Asshown in FIGS. 8 and 9, an illustrative locater comprises a thin writingsurface 40 transparent to light pulses produced by a laser 50 which istranslatable in space to perform a writing function. On the side of thewriting surface 40 remote from the laser 50 are positioned two distinctarrays of fibers. One fiber array 42, the ends of which are depicted aswhite circles in FIG. 8, is used to locate the vertical position(y-axis) of the pen; the second fiber array 44, the ends of which aredepicted as black circles in FIG. 8, is used to locate the horizontalposition (x-axis) of the pen. One set of ends of each array isterminated in a plane parallel to surface 40. Additionally,

as shown in FIG. 9, each fiber of the y-array l2 cornprises a relativelyshort fiber 4l, typically about 5 cm long (about 0.25 ns delay), theends of which correspond to the white circles of FlG. 8. Groups of theshort fibers di are coupled in fan-in fashion through couplers 5l torelatively longer and larger diameter fibers 52 which are cut to produceprescribed delays. Similarly, in the x-array d the short fibers arecoupled in fanin fashion to longer fibers 54 also cut to produceprescribed delays, which however are mutually exclusive from the set ofdelays produced by fibers of the yarray.

Consider, for example, that the y-array d2 and xarray ld each comprisean array of 500 500 short fibers il and that each row of the y-array andeach column of the x-array are fanned-in to ten longer and largerdiameter fibers of the type 52 and 5d. Yl`hat is, in the y-array i2 anyone of the short fibers in the nl" row is coupled to one of l0 longerfibers :5211 each of which produces an n-nanosecond delay t l n 500) tophotodiode do. rhus, in y-array d2. the l0 fibers 52.1 of the first roweach produce a delay of l ns, the l0 fibers 52,2 of the second row eachproduce a delay of 2 ns and in general, 'the l0 fibers 52m of the nIhrow produce an n-nanosecond delay. Similarly, in 'the x-array any one ofthe 500 short fibers il in the mf"- column is coupled to one of l0longer fibers each of which produces a (50G-incr) nanosecond delay t lf1 m 500) to photodiode do., in x-array dit the l0 fibers 54d of thefirst column each produce a delay of 501 ns, the l0 fibers 54.2 ofthesecond column each produce a delay of 502 ns and in general, the l0fibers Shm of the nim-column produce a (500 -lm) nanosecond delay.

Thus. it is apparent that tl y-array i2 has a set of delays from l to500 ns which is mutually exclusive from the set of delays from 50i toi000 ns of the x-array dt. ln addition, as shown in llG. d, the ends ofthe fibers of the two arrays are interleaved so that a light spot 48from laser S0 always overlaps at least two fiber ends, one of which isin the x-array and one of which in the y-array.

As shown in FlG. 9, a light pen including a laser 50, which typicallyemits a l ns pulse every millisecond, is used to write on the writingsurface may also carry on the end of housing a felt E@ which is capableof writing on the surface l0 with an ink transparent to the lightemitted by the laser The light spot 48 on the writing surface l0 made tobe large enough to cover at least two adjacent fibers, one liber fromeach array. As shown in lFlG. l0, when the light pen emits a light spotor pulse at time t: 0, atleast two light pulses propagate to thephotodiode do, The arrival time ty of the first puise Py in the first500 ns interval is proportional to the y-coordinate. The arrival time ofthe second pulse Pm in the 500 to 1000 ns interval is proportional tothe .ir-coordinate. lf the laser spot all?) is large enough, it ispossible as shown in llG. il for the spot to cover two liber ends in thesame row (or column). ln such a case, two pulses PJ., and V1.2 would hereceived by photodiode lo in the interval 500 to 1000 ns. The,ir-coordinate would then be proportional to the average time of arrivalof the two pulses. These arrival times can be electronically coded intobinary bits for transmission over telephone lines or the like by meanswell known in the art.

lt is to be understood that the above described arrangements are merelyillustrative of the many possible specific embodiments which can bedevised to represent application of the principles of our invention.Numerous and varied other arrangements can be devised in accordance withthese principles by those skilled in the art without departing from thespirit and scope of the invention. in particular, where an x-ycoordinate locater with lower resolution (i.e., fewer fibers) isdesired, then it would be possible to utilize a single organ array witheach fiber having a different length corresponding to a separate pointin the r-y plane, and still be able to maintain the differential delaywithin the capabilities of state-of-art electronics and the opticallosses of the longer fibers within tolerable limits.

What is claimed is:

l. An optical sampling oscilloscope for displaying on an electronicdisplay device an optical pulse of duration T less than the risetime TRof said device, comprising, in combination:

l. a passive optical scanner comprising a. means for producing from saidlight pulse of duration T a plurality of light pulses propagating alongspatially separate paths, each of said plurality being substantiallyidentical in transverse shape to the light pulse from which it isproduced,

b. a first array of optical fibers of different lengths with thedifference in length between functionally adjacent fibers being uniform,each of said fibers being arranged so that one end thereof terminates inan input plane and the opposite end thereof terminates in an outputplane, said difference in length producing a substantially uniformdifference in time delay Ar, between functionally adjacent fibers sothat AT1 T, and

c. means for coupling each of said plurality of light pulses intoseparate ones of said fibers at said input plane so that said pluralityof light pulses arrive at said output plane at different times and indifferent spatial locations, thereby to scan said output plane,

Z. said difference AT1 in time delay between said functionally adjacentfibers of said first array being greater than both the rise'time 'rR ofsaid device and the duration T of said optical pulse,

3. means for delaying each of said plurality of spatially separatepulses by uniformly different amounts la-2 less than the duration T ofsaid pulses, said delaying means being disposed betweeen said producingmeans and said first array, an optical gate positioned between saiddelaying means and said first array to receive the spatially separatedand sequentially delayed pulses emanating from said delaying means,

5. control means for opening said gate for a time period equal to asample time ts, coincident in real time but time-wise separated by Argin sampling time, and

6. detecting means for converting said delay pulse samples intoelectrical analogs thereof and for reconstructing a sampled version ofsaid optical pulse on a time scale greater than 'rn for display on saiddevice.

2. The oscilloscope of claim l wherein said delaying means comprising asecond array of optical fibers similar to said first array, the uniformdifference in length of said fibers of said secc/nd array producing auniform difference in delay Arg between functionally adjacent fiberswhich is less than I` and TR, and including cou- 13 pling optics betweensaid gate and said first array for coupling the output of said secondarray to the input of said first array as follows: the tirst fiber inthe second array to the m"l fiber in the first array, the second fiberin the second array to the (rn-l )th ber in the first arl ray, and soon, the delays of the fibers of the second array decreasing indecrements of A12 from the rst fiber to the n" fiber and the delays ofthe fibers of the rst array decreasing in decrements of AT1 from the rstfiber to the mth fiber, where m and n need not necessarily be equal.

3. The oscilloscope of claim 2 wherein said detecting means comprises aphotomultiplier having a risetime of the order of l ns, said devicecomprises an electronic oscilloscope having a risetime of the order of 1ns, and said first and second arrays are arranged so that, respectively,A72 is of the order of a few picoseconds and Ar, is of the order of afew nanoseconds.

4. The oscilloscope of claim 3 wherein the total delay of the longestfiber of said second array is less than l ns and the total delay of theshortest fiber of said first array is greater than 1 ns.

5. The oscilloscope of claim 1 wherein said optical gate comprises: apair of spaced, crossed polarizers, a medium in which birefringence canbe optically induced, said medium being disposed between saidpolarizers, and control pulse means for causing a relatively highintensity, short duration optical control pulse to impinge upon saidmedium when it is desired to sample the pulses emanating from the outputplane of said second array.

6. The oscilloscope of claim 5 wherein said control source comprises apulsed laser for generating control pulses of duration of the order of afew picoseconds or

1. An optical sampling oscilloscope for displaying on an electronicdisplay device an optical pulse of duration T less than the risetime TauR of said device, comprising, in combination:
 1. a passive opticalscanner comprising a. means for producing from said light pulse ofduration T a plurality of light pulses propagating along spatiallyseparate paths, each of said plurality being substantially identical intransverse shape to the light pulse from which it is produced, b. afirst array of optical fibers of different lengths with the differencein length between functionally adjacent fibers being uniform, each ofsaid fibers being arranged so that one end thereof terminates in aninput plane and the opposite end thereof terminates in an output plane,said difference in length producing a substantially uniform differencein time delay Delta Tau 1 between functionally adjacent fibers so thatDelta Tau 1 > T, and c. means for coupling each of said plurality oflight pulses into separate ones of said fibers at said input plane sothat said plurality of light pulses arrive at said output plane atdifferent times and in different spatial locations, thereby to scan saidoutput plane,
 2. said difference Delta Tau 1 in time delay between saidfunctionally adjacent fibers of said first array being greater than boththe risetime Tau R of said device and the duration T of said opticalpulse,
 3. means for delaying each of said plurality of spatiallyseparate pulses by uniformly different amounts Delta Tau 2 less than theduration T of said pulses, said delaying means being disposed betweeensaid producing means and said first array,
 4. an optical gate positionedbetween said delaying means and said first array to receive thespatially separated and sequentially delayed pulses emanating from saiddelaying means,
 5. control means for opening said gate for a time periodequal to a sample time ts, coincident in real time but time-wiseseparated by Delta Tau 2 in sampling time, and
 6. detecting means forconverting said delay pulse samples into electrical analogs thereof andfor reconstructing a sampled version of said optical pulse on a timescale greater than Tau R for display on said device.
 2. said differenceDelta Tau 1 in time delay between said functionally adjacent fibers ofsaid first array being greater than both the risetime Tau R of saiddevice and the duration T of said optical pulse,
 2. The oscilloscope ofclaim 1 wherein said delaying means comprising a second array of opticalfibers similar to said first array, the uniform difference in length ofsaid fibers of said second array producing a uniform difference in delayDelta Tau 2 between functionally adjacent fibers which is less than Tand Tau R, and including coupling optics between said gate and saidfirst array for coupling the output of said second array to the input ofsaid first array as follows: the first fiber in the second array to themth fiber in the first array, the second fiber in the second array tothe (m-1)th fiber in the first array, and so on, the delays of thefibers of the second array decreasing in decrements of Delta Tau 2 fromthe first fiber to the nth fiber and the delays of the fibers of thefirst array decreasing in decrements of Delta Tau 1 from the first fiberto the mth fiber, where m and n need not necessarily be equal.
 3. Theoscilloscope of claim 2 wherein said detecting means comprises aphotomultiplier having a risetime of the order of 1 ns, said devicecomprises an electronic oscilloscope having a risetime of the order of 1ns, and said first and second arrays are arranged so that, respectively,Delta Tau 2 is of the order of a few picoseconds and Delta Tau 1 is ofthe order of a few nanoseconds.
 3. means for delaying each of saidplurality of spatially separate pulses by uniformly different amountsDelta Tau 2 less than the duration T of said pulses, said delaying meansbeing disposed betweeen said producing means and said first array, 4.The oscilloscope of claim 3 wherein the total delay of the longest fiberof said second array is less than 1 ns and the total delay of theshortest fiber of said first array is greater than 1 ns.
 4. an opticalgate positioned between said delaying means and said first array toreceive the spatially separated and sequentially delayed pulsesemanating from said delaying means,
 5. control means for opening saidgate for a time period equal to a sample time Ts, coincident in realtime but time-wise separated by Delta Tau 2 in sampling time, and
 5. Theoscilloscope of claim 1 wherein said optical gate comprises: a pair ofspaced, crossed polarizers, a medium in which birefringence can beoptically induced, said medium being disposed between said polarizers,and control pulse means for causing a relatively high intensity, shortduration optical control pulse to impinge upon said medium when it isdesired to sample the pulses emanating from the output plane of saidsecond array.
 6. The oscilloscope of claim 5 wherein said control sourcecomprises a pulsed laser for generating control pulses of duration ofthe order of a few picoseconds or less.
 6. detecting means forconverting said delay pulse samples into electrical analogs thereof andfor reconstructing a sampled version of said optical pulse on a timescale greater than Tau R for display on said device.